The prior art is replete with television tuner systems, circuits, and components. The tuner is the radio frequency (“RF”) input stage of a television receiver, and the role of the tuner is to select a desired channel while suppressing all other channels and undesired RF signals. The selection is usually accomplished with the use of three tunable filters and one or two fixed filters. The three tunable filters typically utilize a single tuned low loss stage that feeds an amplifier and a higher selectivity, higher loss double tuned stage following the amplifier. The fixed tuned filter(s) follow the down conversion or mixer stage.
It is not practical to tune a stage over the complete frequency range needed to support television reception. Thus, a conventional tuner divides the television frequency range into three bands (UHF, VHFH, and VHFL), each having its own set of tunable filters for a total of nine tunable stages. In normal operation, the channel selection is accomplished by tuning the RF filters to the desired frequency and setting the local oscillator to a frequency that differs from the desired frequency by the intermediate frequency (“IF”) center frequency.
Conventional single conversion television tuners are aligned by physically adjusting a number of coil inductors at the manufacturing facility. The manual alignment procedure, which must be performed for nine tunable filters in many practical tuners, is labor intensive, requires expensive testing equipment, and is costly. In addition, the factory settings of such television tuners may be susceptible to drift caused by age, temperature variation, and physical handling. Due to the fixed nature of such factory settings, excessive drift of the tunable filters may result in a degradation in tuner performance.
Accordingly, it is desirable to have a low cost television tuner circuit that eliminates the need for precision factory alignment. In addition, it is desirable to have a television tuner circuit that will self-align at the time of use or periodically over its lifespan to reduce the adverse effects that would otherwise be caused by component drift and variation. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.